The present invention relates to a water management system for an electrochemical engine in a vehicle.
As electrochemical engines are being integrated into useable vehicles, developing efficient ways of operating it under varying environmental conditions becomes more critical. An electrochemical engine operates by inputting hydrogen gas and oxygen into a fuel cell stack to convert chemical energy into electricity, with water vapor and heat as the primary by-products. Where hydrogen is not stored on board a vehicle, a fuel processor may operate to partially oxidize liquid fuels such as gasoline, diesel, or methanol to produce hydrogen gas. To increase the overall fuel processor efficiency, the fuel processor may also operate as a steam reformer, as processing the fuel with water is inherently more efficient than processing the fuel with air only. Steam reformation releases more hydrogen from water molecules than partial oxidation. Generally, water for steam reformation may be recovered during engine operation, but water may not be available for engine start-up. Initiating engine start-up without water is inefficient, especially in hot environments. The fuel processor is also more difficult to control without water due to the operational window to avoid carbon formation.
To insure that the engine is provided with water for a majority of engine start-ups, water vapor by-product from the fuel cell stack may be cooled through a condenser to recapture liquid water and store it in a reservoir for future engine start-ups. Storing water on board creates the concern for freezing, which may damage associated water supply components such as sensors, valves, and pumps. If the fuel used is methanol for example, the freezing concern may be a non-issue, as water and methanol may be mixed to form a non-freezing mixture. This solution would not work with gasoline-type fuels, which do not naturally form a non-freezing homogeneous mixture with water. Water may be mixed with gasoline as a homogeneous mixture if a surfactant is used; unfortunately most surfactants may add cost and complexity to the fuel infrastructure and affect fuel processor performance.
An alternative solution to the issue of freezing reserved water is to release the water upon turning the vehicle engine off when the temperature approaches freezing. The drawback is that releasing water may cause a potential hazard of creating pools of ice in garages or other parking locations.
Another alternative may be the use of insulating techniques to maintain the water storage tank above freezing.
The present invention is directed to a water management system and a method for operating it in an electrochemical engine. The water management system includes a condenser to recover water from the fuel cell stack exhaust and a water tank to store the recovered water. The recovered water is pumped to the fuel processor upon engine start-up and during normal engine operation to improve engine efficiency. In the event that the temperature threatens to freeze the water in the water tank, a valve opens to release the water to a freeze tank where the water may safely freeze. Removing the water from the water tank minimizes the risk of freezing the associated water system components. A hot exhaust or coolant stream from the electrochemical engine may be passed about the freeze tank to slowly melt the frozen water. In addition or alternatively, the liquid melt may be slowly drained onto the road while the vehicle is in motion.
This water management system takes advantage of the significant efficiencies gained by having water readily available upon start-up of the engine for all temperatures greater than freezing. Although below freezing, the engine starts without water, the condenser is effective at such lower temperatures and quickly forms liquid water to supply to the fuel processor.